Sheet scans

[Prepper]

How often should a sheet be pulled and scanned on a 4-color press running about 5000 an hour? What's a "normal" average? Just for density\color and TVI monitoring throughout the day? Does run length matter? Shorter runs get pulled more often? Longer runs less often?
Thanks

 

[Cornishpastythighs]

couple of questions. Are you running closed loop and how stable is your press. If the density is fluctuating your operators will usually be pulling sheets often to try and keep the press under control and this leads to over control of the process. If the inking system is not in good condition this can cause the operators to 'play the piano' and get more colour variation.
Our operators pull a sheet every few minutes allowing time for any adjustments to have come through the machine. We have both closed loop systems and ink density display systems. Longer runs sheets are not pulled as often as long as the operator is satisfied the process is under control.

 

[Prepper]

It isn't closed loop, 28" Heidelberg, older Tobias scanning densitometer, and an i1 with pressSIGN for color and curves adjustment purposes. I suppose it probably would be more at startup and then stretch out over a longer run as things stabilize? Just trying to get an idea of what a ballpark average might be.

 

[gordo]

Measure SIDs. When you hit your SIDs the presswork should align with your proof. Don't bother measuring TVI - unless something looks terrible wrong. In which case the job should be pulled off the press and TVI used as one of the diagnostic tools to find out why. The press operator is better off looking for artefacts like hickeys, specks, etc. in the presswork. Once you're up to color, with a press run of 5000, you might only have time for a couple of three pulls to check SIDs and artefacts - depending on how fast you're running the press.

 

[turbotom1052]

if the plates are spot on the job should almost "fall" into color and stay there with little operator intervention once you've got ink water balance. Ive found that when I struggle with color during the makeready, you can count on chasing color throughout the run. Each press in the shop should be fingerprinted and checked periodically, so that you can feel confident that the press is printing whats on the plates, and conversely so that the prepress dept is outputting accurate plates. It should be noted that prepress curves are not interchangeable between multiple presses if you want the best results.

 

[DanColor]

On average, you are looking at around 3 pulls for start up.

The first couple are to ensure ink/water balance is achieved before going through with the run. Any additional pulls are for adjustments on press to match your proof or to make the job more stable. The number of pulls needed for this really depend on the presses capability to hit your proof standard after reaching SID. Most of the time adjustments need to be made as a press won't hit the proof with SID alone. Typically press conditions will have drifted from the standard leaving you to spend more time at make-ready doing adjustments.

For longer runs, you'll be making pulls every so often to double check the process is stable.